High-quality sgoi by annealing near the alloy melting point

ABSTRACT

A method of forming a low-defect, substantially relaxed SiGe-on-insulator substrate material is provided. The method includes first forming a Ge-containing layer on a surface of a first single crystal Si layer which is present atop a barrier layer that is resistant to Ge diffusion. A heating step is then performed at a temperature that approaches the melting point of the final SiGe alloy and retards the formation of stacking fault defects while retaining Ge. The heating step permits interdiffusion of Ge throughout the first single crystal Si layer and the Ge-containing layer thereby forming a substantially relaxed, single crystal SiGe layer atop the barrier layer. Moreover, because the heating step is carried out at a temperature that approaches the melting point of the final SiGe alloy, defects that persist in the single crystal SiGe layer as a result of relaxation are efficiently annihilated therefrom. In one embodiment, the heating step includes an oxidation process that is performed at a temperature from about 1230° to about 1320° C. for a time period of less than about  2  hours. This embodiment provides SGOI substrate that have minimal surface pitting and reduced crosshatching.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/855,915, filed May 27, 2004 which is a continuation-in-part (CIP)application of U.S. patent application Ser. No. 10/448,948, filed May30, 2003 and is related to co-pending and co-assigned U.S. patentapplication Ser. No. 10/055,138, filed Jan. 23, 2002, entitled “Methodof Creating High- Quality Relaxed SiGe-On-Insulator for Strained Si CMOSApplications”, as well as co-pending and co-assigned U.S. patentapplication Ser. No. 10/196,611, filed Jul. 16, 2002, entitled “Use OfHydrogen Implantation To Improve Material Properties OfSilicon-Germanium-On-Insulator Material Made By Thermal Diffusion”, theentire contents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method of fabricating a semiconductorsubstrate material, and more particularly to a method of fabricating alow-defect, substantially relaxed SiGe-on-insulator (SGOI) substratematerial. In one embodiment, a method is provided that can form alow-defect, substantially relaxed SGOI substrate in which surfacepitting and crosshatching have been substantially reduced. Thelow-defect, substantially relaxed SiGe-on-insulator substrate materialof the present invention can be used as a lattice mismatched templatefor creating a strained Si layer thereon by subsequent Si epitaxialovergrowth. Such a substrate material is desired for the enhanced chargecarrier transport properties within a strained Si layer and is acandidate for future high performance complementary metal oxidesemiconductor (CMOS) applications. The present invention is alsodirected to a SiGe-on-insulator substrate material as well as structureswhich include at least the substrate material.

BACKGROUND OF THE INVENTION

In the semiconductor industry, there has recently been a high-level ofactivity using strained Si-based heterostructures to achieve highmobility structures for CMOS applications. Traditionally, the prior artmethod to implement this has been to grow strained Si layers on thick(on the order of from about 1 to about 5 micrometers) relaxed SiGebuffer layers.

Despite the high channel electron mobilities reported for prior artheterostructures, the use of thick SiGe buffer layers has severalnoticeable disadvantages associated therewith. First, thick SiGe bufferlayers are not typically easy to integrate with existing Si-based CMOStechnology. Second, the defect densities, including threadingdislocations (TDs) and misfit dislocations, are from about 10⁵ to about10⁸ defects/cm² which are still too high for realistic VSLI (very largescale integration) applications. Thirdly, the nature of the prior artstructure precludes selective growth of the SiGe buffer layer so thatcircuits employing devices with strained Si, unstrained Si and SiGematerials are difficult, and in some instances, nearly impossible tointegrate.

In order to produce relaxed SiGe material on a Si substrate, prior artmethods typically grow a uniform, graded or stepped, SiGe layer tobeyond the metastable critical thickness (i.e., the thickness beyondwhich dislocations form to relieve stress) and allow misfit dislocationsto form, with the associated threading dislocations, through the SiGebuffer layer. Various buffer structures have been used to try toincrease the length of the misfit dislocation section in the structuresand thereby to decrease the TD density.

In addition to the TDs that form during the relaxation process, stackingfaults (SF) have been observed to form under certain strain andannealing conditions; see R. Hull and J. C. Bean, J. Vac. Sci. Technol.,Vol. 7 (4), 1989, pg. 2580. It is believed that the presence of a SFdefect within a semiconductor material represents a more significantthreat to proper electrical behavior of the material compared to anisolated TD.

Another prior art approach, such as described in U.S. Pat. Nos.5,461,243 and 5,759,898, both to Ek, et al., provides a structure with arelaxed and reduced defect density semiconductor layer wherein a newstrain relief mechanism operates whereby the SiGe buffer layer relaxeswhile reducing the generation of TDs within the SiGe layer.

Co-pending and co-assigned U.S. patent application Ser. No. 10/055,138,filed Jan. 23, 2002, entitled “Method of Creating High-Quality RelaxedSiGe-On-Insulator for Strained Si CMOS Applications” provides a uniqueway of fabricating high-quality, substantially relaxed SiGe-on-insulatorsubstrates. In the '138 application, a high-quality, substantiallyrelaxed SiGe alloy layer is formed atop a first single crystal Si layerby first forming a SiGe or pure Ge layer on the surface of the firstsingle crystal Si layer, which is present atop a barrier layer that isresistance to Ge diffusion, and then heating the layers at a temperaturethat permits interdiffusion of Ge throughout the first single crystal Silayer and the SiGe or pure Ge layer thereby forming a substantiallyrelaxed, single crystal SiGe layer atop the barrier layer. The heatingstep is performed at various temperatures and a statement is madetherein that a tailored heat cycle that is based upon the melting pointof the SiGe layer may be used. Specifically, the '138 application statesthat “the temperature is adjusted to tract below the melting point ofthe SiGe layer”.

The '138 application provides no specifics about the tailored heatcycle, other than the temperature is adjusted below the melting point ofthe SiGe. Additionally, no recognition was made in that disclosure whichindicates that the tailored heat cycle could be used as a means ofsubstantially reducing the residual defect density in the SiGe alloylayer. Moreover, the disclosure of the '138 application does notrecognize that the bulk of the oxidation anneal process should becarried out at or near the melting point of SiGe. Furthermore, thedisclosure of the '138 application does not recognize that thetemperature of the tailored heating cycle could be adjusted so as toeliminate specific types of defects.

SGOI substrates formed using the thermal mixing process disclosed in the'138 application rely on a high-temperature oxidation to form ahomogeneous SiGe alloy over an insulating layer. Under certainconditions, the surface of the SiGe alloy will begin to form micropits(i.e., microdivots) that can degrade the surface quality of thematerial. Inasmuch as SGOI substrates are used as a template forfabricating strained Si high-performance CMOS devices, it is imperativethat the surface quality of the relaxed SiGe alloy layer be made as highas possible, in terms of smoothness and low defect density artifacts.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a method offabricating thin, high-quality, substantially relaxed SiGe-on-insulatorsubstrate materials in which the SiGe layer has a low-defect density, onthe order of about 10⁷ defects/cm² or less.

Another object of the present invention is to provide a method offabricating thin, high-quality, substantially relaxed SiGe-on-insulatorsubstrate materials in which a heating step is employed that is capableof substantially reducing the threading defect density in the SiGe alloylayer.

Still another object of the present invention is to provide a method offabricating thin, high-quality, substantially relaxed SiGe-on-insulatorsubstrate materials in which a heating step is employed that is capableof substantially reducing (compared to prior art methods) the stackingfault defect density in the SiGe alloy layer.

A further object of the present invention is to provide a method offabricating thin, high-quality, substantially relaxed SiGe-on-insulatorsubstrate materials in which a heating step is performed underconditions that efficiently annihilate existing defects, while retardingthe formation of certain defects in the SiGe alloy layer as a result ofrelaxation of the initially strained SiGe.

A yet farther object of the present invention is to provide a method offabricating thin, high-quality, low-defect density, substantiallyrelaxed SiGe-on-insulator substrate materials, which is compatible withCMOS processing steps.

An even further object of the present invention is to provide a methodof fabricating thin, high-quality, low-defect density, substantiallyrelaxed SiGe-on-insulator substrate materials which can be used aslattice mismatched templates, i.e., substrates, for forming strained Silayers.

A still further object of the present invention is to provide strainedSi/substantially relaxed SiGe-on-insulator structures that have highcarrier mobility and are useful in high-performance CMOS applications.

An additional object of the present invention is to provide a method ofcreating a SGOI substrate having minimized surface pitting and reducedcrosshatching as compared to prior art SGOI substrates made by thethermal mixing process of the '138 application.

These and other objects and advantages are achieved in the presentinvention by utilizing a method which includes first forming aGe-containing layer, such as a SiGe alloy or pure Ge, on a surface of afirst single crystal Si layer, said first single crystal Si layer ispresent atop a barrier layer that is resistant to Ge diffusion; andthereafter a heating step is performed at a temperature that approaches(i.e., at or near) the melting point of the SiGe alloy while retainingGe, but not less than the temperature required to retard SF defectgeneration; the variation from the actual melting point of a specific Gecontent SiGe alloy may be slightly less, on the order of −50° C., fromthe actual melting point of the SiGe alloy while greater than about1230° C. to retard SF generation.

The heating step of the present invention permits interdiffusion of Gethroughout the first single crystal Si layer and the Ge-containing layerthereby forming a substantially relaxed, single crystal SiGe layer atopthe barrier layer. Moreover, because the heating step of the present iscarried out at a temperature that approaches the melting point of thefinal single crystal SiGe layer, defects that persist in the singlecrystal SiGe layer as a result of relaxation are efficiently annihilatedtherefrom. Oxidation performed at temperatures ≧1230° C. also retardsthe formation of SF defects within the SiGe layer. It is noted that thesubstantially relaxed, single crystal SiGe layer is comprised of ahomogeneous mixture of the Ge-containing layer as well as the firstsingle crystal Si layer.

In one embodiment of the present invention, it has been determined thata high-quality, substantially relaxed SGOI substrate having improvedsurface characteristics (minimal surface pitting and reducedcrosshatching) can be produced by utilizing a heating step in which theoxidation is performed at a temperature from about 1230° to about 1320°C. for a time period of less than about 2 hours. The term“crosshatching” is used throughout the present application to denote thehigh frequency component of the surface roughness (power spectrum) asmeasured by Atomic Force Microscopy (AFM).

When this embodiment of the present invention is employed, the presentinvention achieves an advantage over the prior art by minimizing surfacepitting which occurs when SGOI substrates are formed by prolongedoxidation or annealing at high temperatures (greater than 1230° C.).Specifically, an oxidation temperature within the range of about 1230°to about 1320° C. was found to be sufficient to increase the surfacemobility of the Si and Ge atoms to an extent where the surfacecrosshatching which results from the relaxation of the SiGe is reduced.The subsequent pitting which occurs as an undesirable side effect of theincreased surface mobility is minimized by reducing the oxidation timeat high oxidation temperatures. By using this particular embodiment ofthe present invention, it is possible to form high-quality SGOIsubstrates with minimal surface pitting and reduced crosshatching.

Following the above steps of the present invention, a strained Si layermay be grown epitaxially atop the substantially relaxed single crystalSiGe layer to form a strained Si/relaxed SiGe-containing heterostructurethat can be used in a variety of high-performance CMOS applications.

In some embodiments of the present invention, the first single crystalSi and barrier layer are components of a silicon-on-insulator (SOI)substrate. In other embodiments, the barrier layer is formed atop asurface of a semiconductor substrate, and thereafter the first singlecrystal Si layer is formed atop the barrier layer. The latter substratematerial is a non-SOI substrate.

The present method also contemplates the use of barrier layers that areunpatterned (i.e., barrier layers that are continuous) or patterned(i.e., discrete and isolated barrier regions or islands which aresurrounded by semiconductor material).

In yet another embodiment of the present invention, a Si cap layer isformed atop the Ge-containing layer prior to heating the structure at ornear the melting point of the final SiGe layer. This embodiment of thepresent invention alters the thermodynamic stability (in terms ofpreventing defect production) of the SiGe layer before annealing. TheSiGe layer has a thickness of about 2000 nm or less, with a thickness offrom about 10 to about 200 nm being more highly preferred.

In still yet another embodiment of the present invention, an ionimplantation step may be performed prior to heating.

Another aspect of the present invention relates to the SiGe-on-insulatorsubstrate material that is formed utilizing the above-mentionedprocessing steps. Specifically, the inventive substrate materialcomprises a Si-containing substrate; an insulating region that isresistant to Ge diffusion present atop the Si-containing substrate; anda substantially relaxed SiGe layer present atop the insulating region,wherein the substantially relaxed SiGe layer has a thickness of about2000 nm or less and a defect density of about 10⁷ defects/cm² or less.

In the embodiment in which the oxidation is performed at a temperaturefrom about 1230° to about 1320° C. for a time period of less than about2 hours, a SGOI substrate is formed in which the surface roughness isless than about 15 Å RMS. Such a surface roughness is indicative of aSGOI substrate that has minimal surface pitting and reducedcrosshatching. By “minimal surface pitting” it is meant a SiGe surfacehaving a pit depth that is below 30 Å and a width that is below 300 nm.The term “minimized crosshatching” denotes a SiGe surface that has areduced component of the roughness caused by surface steps (formed bydislocation movement during relaxation of the SiGe layer) as compared toSGOI formed at 1200° C. and below. The surface pitting and crosshatchingcan be determined by AFM (Atomic Force Microscopy) or other relatedtechniques.

A yet further aspect of the present invention relates to aheterostructure which includes at least the above-mentioned substratematerial. Specifically, the heterostructure of the present inventioncomprises a Si-containing substrate; an insulating region that isresistant to Ge diffusion present atop the Si-containing substrate;

a substantially relaxed SiGe layer present atop the insulating region,wherein the substantially relaxed SiGe layer has a thickness of about2000 nm or less and a defect density of about 10⁷ atoms/cm² or less; anda strained Si layer formed atop the substantially relaxed SiGe layer.

The heterostructure may also include a SGOI substrate that has minimalsurface pitting and reduced crosshatching.

Other aspects of the present invention relate to superlattice structuresas well as templates for other lattice mismatched structures whichinclude at least the SiGe-on-insulator substrate material of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E are pictorial representations (through cross-sectionalviews) showing the basic processing steps that are employed in thepresent invention in fabricating a thin, high-quality, substantiallyrelaxed SiGe-on-insulator substrate material wherein the initialsubstrate includes an unpatterned diffusion barrier region.

FIGS. 2A-E are pictorial representations (through cross-sectional views)showing the basic processing steps that are employed in an alternativeembodiment of the present invention in fabricating a thin, high-quality,substantially relaxed SiGe-on-insulator substrate material wherein theinitial substrate includes a patterned diffusion barrier region.

FIGS. 3A-3B are pictorial representations (through cross-sectionalviews) showing an alternative embodiment of the present inventionwherein a Si cap layer is formed atop a Ge or SiGe layer which is formedon an unpatterned (3A) or patterned (3B) substrate.

FIGS. 4A-4B are pictorial representations (through cross-sectionalviews) showing the formation of a strained Si layer on the thin,high-quality, substantially relaxed SiGe-on-insulator substrate materialof FIGS. 1E and 2E, respectively.

FIG. 5 is a graph showing the melting point vs. Ge content of a SiGebinary alloy system The S denotes a solid, the L is a liquid, and thearea between the two curves is the transition phase between solid andliquid.

FIG. 6 is a plan-view TEM micrograph of a 600 Å, 17% SiGe-on-insulatorsubstrate material prepared using a heating step in which thetemperature was 100° C. below the melting point of a 26% SiGe alloy.

FIG. 7 is a plan-view TEM micrograph of a 60 nm 17% SiGe-on-insulatorsubstrate prepared using the processing steps of the present invention,i.e., prepared using a heating step in which the temperature is at ornear the melting point of a 19% SiGe alloy.

FIG. 8 is a graph of measured MF/SF density vs. SGOI thickness forvarious samples heated at different temperatures.

FIG. 9 is a 10×10 μm Atomic Force Microscope image of an SGOI substrateformed using a prior art thermal mixing process at an oxidationtemperature of about 1200° C.; crosshatching is visible.

FIG. 10 is a 10×10 μm Atomic Force Microscope image of an SGOI substrateformed using the inventive process at an oxidation temperature of about1250° C. for 30 minutes; crosshatching has been minimized.

FIG. 11 is a plot of divot depth (measured by AFM) vs. oxidation timefor 1250° C. oxidation temperature used to form a 400 Å 25% (Ge content)SGOI layer. The initial film structure and the thickness of the grownsurface oxide is the same in all cases. Pitting is minimized for shorteroxidation times.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a method of fabricating thin,high-quality, substantially relaxed SiGe-on-insulator substratematerials which can then serve as a lattice mismatched template forsubsequent overgrowth of epitaxial Si, will now be described in greaterdetail by referring to the drawings that accompany the presentapplication. In the accompanying drawings, like and/or correspondingelements are referred to by like reference numerals.

The present application provides a direct approach to the formation oflow-defect, substantially relaxed SiGe-on-insulator substrate materialswhereby the heating step of the present invention is performed at atemperature approaching the melting point of the SiGe alloy, while highenough to retard SF formation. The result of the controlled heatingstep, which is performed at or near the melting point of the finalrelaxed SiGe alloy layer, is a reduction in the residual defect densitycompared to similar layers that are annealed at lower temperatures.

Reference is first made to FIGS. 1A and 2A, which show initial substratematerials that can be employed in the present invention. Specifically,the initial substrate materials illustrated in FIGS. 1A and 2A eachcomprise a Si-containing semiconductor substrate 10, a barrier layer 12which is resistant to Ge diffusion (hereinafter “barrier layer”) presentatop a surface of the Si-containing semiconductor substrate 10 and afirst single crystal Si layer 14 having misfit and TD densities of lessthan about 1×10⁴ defects/cm² present atop the barrier layer 12. In thedrawings, reference numeral 17 denotes the interface between the barrierlayer 12 and the first single crystal Si layer 14.

The difference between the two initial structures depicted in thedrawings is that, in FIG. 1A, the barrier layer 12 is presentcontinuously throughout the entire structure, whereas in FIG. 2A, thebarrier layer 12 is present as discrete and isolated regions or islandsthat are surrounded by semiconductor material, i.e., layers 10 and 14.The initial structure shown in FIG. 1A includes an unpatterned barrierlayer, whereas the initial structure of FIG. 2A includes a patternedbarrier layer.

Notwithstanding whether the barrier layer 12 is patterned orunpatterned, the initial structure may be a conventionalsilicon-on-insulator (SOI) substrate material wherein region 12 is aburied oxide region which electrically isolates the first single crystalSi layer 14 from the Si-containing substrate semiconductor substrate 10.The term “Si-containing” as used herein denotes a semiconductorsubstrate that includes at least silicon. Illustrative examples include,but are not limited to: Si, SiGe, SiC, SiGeC, Si/Si, Si/SiC, Si/SiGeC,and preformed silicon-on-insulators which may include any number ofburied oxide (continuous, non-continuous or mixtures of continuous andnon-continuous) regions present therein.

The SOI substrate may be formed utilizing conventional SIMOX (separationby ion implantation of oxygen) processes well known to those skilled inthe art, as well as the various SIMOX processes mentioned in co-assignedU.S. patent applications Ser. Nos. 09/861,593, filed May 21, 2001;09/861,594, filed May 21, 2001; 09/861,590, filed May 21, 2001;09/861,596, filed May 21, 2001; and 09/884,670, filed Jun. 19, 2001 aswell as U.S. Pat. No. 5,930,634 to Sadana, et al., the entire contentsof each are incorporated herein by reference. Note that the processdisclosed in the '590 application can be employed herein to fabricatethe patterned substrate shown in FIG. 2A. Alternatively, the SOIsubstrate material may be made using other conventional processesincluding, for example, a thermal bonding and layer transfer process.

In addition to SOI substrates, the initial substrates shown in FIGS. 1Aand 2A maybe a non-SOI substrate that is made using conventionaldeposition processes as well as lithography and etching (employed whenfabricating a patterned substrate). Specifically, when non-SOIsubstrates are employed, the initial structure is formed by depositing aGe diffusion barrier layer atop a surface of a Si-containing substrate,via conventional deposition or thermal growing processes, optionallypatterning the barrier layer by employing conventional lithography andetching; and thereafter forming a single crystal Si layer atop thebarrier layer using conventional deposition processes including chemicalvapor deposition (CVD), plasma-assisted CVD, sputtering, evaporation,chemical solution deposition or epitaxial Si growth.

Barrier layer 12 of the initial structure shown in FIGS. 1A and 2Acomprises any insulating material that is highly resistant to Gediffusion. Examples of such insulating and Ge diffusion resistantmaterials include, but are not limited to: crystalline ornon-crystalline oxides or nitrides.

The thickness of the various layers of the initial structure may varydepending on the process used in making the same. Typically, however,the single crystal Si layer 14 has a thickness of from about 1 to about2000 nm, with a thickness of from about 20 to about 200 nm being morehighly preferred. In the case of the barrier layer 12 (i.e., Gediffusion resistant layer), that layer may have a thickness of fromabout 1 to about 1000 nm, with a thickness of from about 20 to about 200nm being more highly preferred. The thickness of the Si-containingsubstrate layer, i.e., layer 10, is inconsequential to the presentinvention. The thicknesses provided above are exemplary and by no wayslimit the scope of the present invention.

FIGS. 1B and 2B illustrate the structure that is formed after aGe-containing layer 16 is formed atop the first single crystal Si layer14. The Ge-containing layer 16 includes a SiGe alloy or pure Ge. Theterm “SiGe alloy” includes SiGe materials that comprise up to 99.99atomic percent Ge, whereas pure Ge includes layers that comprise 100atomic percent Ge. When SiGe layers are employed, it is preferred thatthe Ge content in the SiGe layer be from about 0.1 to about 99.9 atomicpercent, with a Ge atomic percent of from about 10 to about 35 beingeven more highly preferred. The SiGe alloys may be single-crystal,amorphous or polycrystalline.

In accordance with the present invention, the Ge-containing layer 16 isformed atop the first single crystal Si layer 14 using any conventionalepitaxial growth method that is well known to those skilled in the artwhich is capable of (i) growing a thermodynamically stable (below acritical thickness) Ge-containing layer, (ii) growing a Ge-containinglayer that is metastable and free from defects, i.e., misfit and TDdislocations, or (iii) growing a partially or fully relaxed SiGe layer;the extent of relaxation being controlled by growth temperature, Geconcentration, thickness, or the presence of a Si capping layer.Illustrative examples of such epitaxial growing processes that arecapable of satisfy conditions (i), (ii), or (iii) include, but are notlimited to: low-pressure chemical vapor deposition (LPCVD), ultra-highvacuum chemical vapor deposition (UHVCVD), atmospheric pressure chemicalvapor deposition (APCVD), molecular beam (MBE) epitaxy andplasma-enhanced chemical vapor deposition (PECVD).

The thickness of the Ge-containing layer 16 formed at this point of thepresent invention may vary, but typically the Ge-containing layer 16 hasa thickness of from about 10 to about 500 nm, with a thickness of fromabout 20 to about 200 nm being more highly preferred.

In an alternative embodiment of the present invention, see FIGS. 3A-3B,an optional cap layer 18 is formed atop the Ge-containing layer 16 priorto performing the heating step of the present invention. The optionalcap layer 18 employed in the present invention comprises any Si materialincluding, but not limited to: epitaxial silicon (or SiGe) (epi-Si),amorphous silicon (a:Si), amorphous SiGe, single or polycrystalline Sior any combination thereof including multilayers. In a preferredembodiment, the cap layer is comprised of epi Si. It is noted thatlayers 16 and 18 may, or may not, be formed in the same reactionchamber.

When present, the optional cap layer 18 has a thickness of from about 1to about 100 nm, with a thickness of from about 1 to about 30 nm beingmore highly preferred. The optional cap layer 18 is formed utilizing anywell-known deposition process including the epitaxial growth processesmentioned above.

In one embodiment of the present invention, it is preferred to form aGe-containing layer (15 to 20 atomic percent Ge) having a thickness offrom about 1 to about 2000 nm on the surface of a single crystal Silayer, and thereafter forming a Si cap layer having a thickness of fromabout 1 to about 100 nm atop the Ge-containing layer.

After forming the Ge-containing layer 16 (with or without the optionalcap layer 18) atop the initial structure, the structure shown in eitherFIG. 1B or 2B (with or without the optional cap) may then be subjectedto an optional ion implantation step wherein ions that are capable offorming defects that allow enhanced relaxation at or near the interface17 is performed. Examples of such defects that permit enhancedrelaxation to occur include: platelet defects or bubble-like defects, asin the case for hydrogen ion implantation. The implant may be performedwith or without the use of an implantation mask.

The structure after this implantation step is shown in FIG. 1C or 2C. Inthese figures, reference numeral 19 denotes the defect regions formed bythe ion implantation step. The defect regions solve the problem ofdefect production in the SiGe alloy/single crystal Si bilayer byfacilitating relaxation of the bilayer to occur. Specifically,relaxation occurs by plastically deforming the defect region that ispresent at or near the interface 17.

The defects, which permit enhanced relaxation to occur at or near theinterface 17, are formed by implanting ions such as hydrogen, deuterium,helium, oxygen, fluorine, neon, and mixtures thereof into the variouslayers using implant conditions which maintain the peak of the ion rangeat or near interface 17. Isotopes of the aforementioned ions are alsocontemplated herein. Preferred ions used in the present invention arehydrogen ions (H⁺). It is noted that other species of hydrogen such asH₂ ⁺ can also contemplated herein.

The implant step of the present invention is conducted at approximatelyroom temperature, i.e., a temperature of from about 283K to about 303K,using a beam current density of from about 0.01 to about 10microamps/cm². Implantation at different temperatures and/or using otherbeam current densities may affect the relaxation behavior.

The concentration of the implant species used in forming the plateletdefects may vary depending upon the type of implant species employed.Typically, however, the concentration of implanting ions used at thispoint of the present invention is below 3E16 cm⁻², with an ionconcentration of from about 1E16 to about 2.99E16 cm⁻² being more highlypreferred. The energy of this implant may also vary depending upon thetype of ion that is being implanted, with the proviso that the implantenergy must be capable of positioning ions at or near interface 17. Forexample, when hydrogen is employed as the implant ion, the energy usedto ensure platelet formation at or near interface 17 is from about 1 toabout 100 keV, with an energy of from about 3 to about 20 keV being morehighly preferred.

The implantation of the foregoing energetic ions into or near thestrained SiGe/Si interface creates defects that can serve as efficientdislocation nucleation sites which allow the SiGe layer to relax moreefficiently. The randomness of the defect sites caused by thisimplantation also reduces defect pinning caused by interactions betweenmoving dislocations and thereby makes the relaxation process moreefficient.

After forming the Ge-containing layer 16 (with or without the optionalcap layer 18 and with or without the implant) atop the initialstructure, the structure (with or without the optional cap layer 18 andwith or without the implant) is then heated, i.e., annealed, at atemperature which substantially annihilates defects caused by strainedrelaxation, while permitting interdiffusion of Ge throughout the firstsingle crystal Si layer 14, the Ge-containing layer 16 and, if present,the optional Si cap 18 thereby forming a substantially relaxed, singlecrystal SiGe layer 20 atop the barrier layer 12. Note that an oxidelayer 22 is formed atop the SiGe layer 20 during the heating step. Oxidelayer 22 is typically, but not always, removed from the structure afterthe heating step using a conventional wet etch process wherein achemical etchant such as HF that has a high selectivity for removingoxide as compared to SiGe is employed. The resultant structure formedafter the heating step has been performed is shown, for example in FIGS.1D or 2D.

Note that when the oxide layer 22 is removed, a second single crystal Silayer can be formed atop the SiGe layer 20 and the above processingsteps of the present invention may be repeated any number of times toproduce a multilayered relaxed SiGe substrate material.

The oxide layer 22 formed after the heating step of the presentinvention has a variable thickness which may range from about 10 toabout 1000 nm, with a thickness of from about 20 to about 500 nm beingmore highly preferred.

Specifically, the heating step of the present invention is an annealingstep that is performed at a temperature that is at or near the meltingpoint of a selected SiGe alloy, yet at a temperature high enough toretard the formation of SF defects. The selected SiGe alloy is based onthe Ge content desired in the final relaxed SiGe layer. FIG. 5 is agraph showing the melting point vs. Ge content of a SiGe binary alloysystem. The S denotes a solid, the L is a liquid, and the area betweenthe two curves is the transition phase between solid and liquid. Thetemperature of the heating step of the present invention substantiallytracts along the bottom curve in the drawing, which is labeled as T₁ forconvenience. The temperature used in the heating step of the presentinvention may be slightly less than the actual melting point for a givenGe content.

Specifically, the heating temperature may be performed at the actualmelting point of a selected SiGe alloy layer or at a temperature ofabout 50° C. below the actual melting point but above about 1230° C. toreduce SF defect generation during oxidation. Care should be taken notto heat the structure in the area between the two curves sinceagglomeration of the SiGe alloy can occur if heating occurs within thatarea. The heating step of the present invention, which is a function ofGe content, may be performed at a temperature of from about 1230° C.(for 30% Ge) to about 1410° C. (for 0.1% Ge in a SiGe alloy).

Moreover, the heating step of the present invention is carried out in anoxidizing ambient which includes at least one oxygen-containing gas suchas O₂, NO, N₂O, ozone, air and other like oxygen-containing gases. Theoxygen-containing gas may be admixed with each other (such as anadmixture of O₂ and NO), or the gas may be diluted with an inert gassuch as He, Ar, N₂, Xe, Kr, or Ne.

The heating step may be carried out for a variable period of time whichtypically ranges from about 10 to about 1800 minutes, with a time periodof from about 30 to about 600 minutes being more highly preferred. Theheating step may be carried out at a single targeted temperature, orvarious ramp and soak cycles using various ramp rates and soak times canbe employed. A soak step may be used below the actual melting point of agiven SiGe alloy to tailor the types of defects present in thestructure.

The heating step is performed under an oxidizing ambient to achieve thepresence of a surface oxide layer, i.e., layer 22, which acts as adiffusion barrier to Ge atoms. Therefore, once the oxide layer is formedon the surface of the structure, Ge becomes trapped between the barrierlayer 12 and the oxide layer 22. As the surface oxide increases inthickness, the Ge becomes more uniformly distributed throughout layers14, 16, and optionally 18, but it is continually and efficientlyrejected from the encroaching oxide layer. So as the (now homogenized)layers are thinned during this heating step, the relative Ge fractionincreases.

It has been determined in the present invention, that the bulk of theoxidation be carried out at or above approximately 1230° C. to reducethe generation of SF defects as the SiGe layer is thinned. Therefore, itis contemplated that temperature be ramped down under dilute-oxygen ornon-oxidizing ambient so as to avoid an increase in the generation rateof SF defects as a result of oxidation below about 1230° C. Theoxidation temperature being between 1230 and 1350° C.; with 1250 to1325° C. being more highly preferred.

Note that if the oxidation occurs too rapidly, Ge cannot diffuse awayfrom the surface oxide/SiGe interface fast enough and is eithertransported through the oxide (and lost) or the interfacialconcentration of Ge becomes so high that the alloy melting temperaturewill be reached.

The role of the heating step of the present invention is (1) toannihilate defects formed from strain relaxation; (2) allow Ge atoms todiffuse more quickly thereby maintaining a homogeneous distributionduring annealing; and (3) to subject the initial layer structure to athermal budget which will facilitate an equilibrium configuration insuch a way as to minimize the number of defects generated duringoxidation. After this heating step has been performed, the structureincludes a uniform and substantially relaxed, low-defect SiGe alloylayer, i.e., layer 20, sandwiched between the barrier layer 12 andsurface oxide layer 22. See FIGS. 1D or 2D.

In one embodiment of the present invention, the oxidation temperature iscontrolled within a range from about 1230° to about 1320° C. and theoxidation is performed for a time period of less than about 2 hours.More preferably, the oxidation is performed at a temperature from about1230° to about 1300° C. for a time period of less than about 1.5 hours.When this embodiment of the present invention is performed, ahigh-quality, substantially relaxed SGOI substrate having improvedsurface characteristics (in terms of surface pitting and crosshatching)is provided. The SOI substrate provided using this embodiment of thepresent invention has a surface roughness that is less than 15 Å RMS, apit depth of less than 30 Å and a pit width of less than 300 nm. Thisembodiment of the present invention can be used in conjunction with thevarious embodiments mentioned hereinabove.

In accordance with the present invention, the relaxed SiGe layer 20 hasa thickness of about 2000 nm or less, with a thickness of from about 10to about 100 nm being more highly preferred. Note that the relaxed SiGelayer 20 formed in the present invention is thinner than prior art SiGebuffer layers and has a TD density of from about 2 to 10 times lowerthan SGOI formed at 1200° C. and a SF defect density reduction by abouta factor of 100. See FIG. 8. This represents a two order of magnitudereduction in the defect density as compared to the process disclosed inthe '138 application.

The relaxed SiGe layer formed in the present invention has a final Gecontent of from about 0.1 to about 30 atomic percent, with an atomicpercent of Ge of from about 10 to about 30 being more highly preferred.Another characteristic feature of relaxed SiGe layer 22 is that it has ameasured lattice relaxation of from about 1 to about 99%, with ameasured lattice relaxation of from about 50 to about 80% being morehighly preferred.

As stated above, the surface oxide layer 22 may be stripped at thispoint of the present invention so as to provide the SiGe-on-insulatorsubstrate material shown, for example, in FIGS. 1E or 2E (note that thesubstrate material does not include the cap layer since that layer hasbeen used in forming the relaxed SiGe layer).

FIGS. 4A-B show the structure that is obtained after forming Si layer 24atop SiGe layer of FIGS. 1E and 2E, respectively. Si layer 24 is formedusing a conventional epitaxial deposition process well known in the art.The thickness of the epi-Si layer 24 may vary, but typically, the epi-Silayer 24 has a thickness of from about 1 to about 100 nm, with athickness of from about 1 to about 30 nm being more highly preferred.

In some instances, additional SiGe can be formed atop the relaxed SiGelayer 20 utilizing the above-mentioned processing steps, and thereafterthe epi-Si layer 24 may be formed. Because layer 20 has a large in-planelattice parameter as compared to the epi-Si layer 24, epi-Si layer 24will be strained in a tensile manner.

As stated above, the present invention also contemplates superlatticestructures as well as lattice mismatched structures which include atleast the SiGe-on-insulator substrate material of the present invention.In the case of superlattice structures, such structures would include atleast the substantially relaxed SiGe-on-insulator substrate material ofthe present invention, and alternating layers Si and SiGe formed atopthe substantially relaxed SiGe layer of the substrate material.

In the case of lattice mismatched structures, GaAs, GaP or other likecompound would be formed atop the substantially relaxed SiGe layer ofthe inventive SiGe-on-insulator substrate material.

An example of the defect reduction using the method of the presentinvention is illustrated in FIGS. 6 (Prior Art) and 7 (Invention). Theinitial structure, in each case, was a 600 Å, 17% pseudomorphicallystrained SiGe alloy grown on a 550 Å Si SIMOX SO wafer. FIG. 6 showsplan-view TEM micrograph results of the sample that was thermally mixedand oxidized at 1200° C. to a final Ge content of 26%. The heating,which is in accordance with the '138 application, was about 100° C. lessthan the melting point of the SiGe alloy layer. The defect density wasabout 5E7 cm⁻² threading defects and some misfit segments (or stackingfaults) were evident. FIG. 7 shows plan-view TEM micrograph results ofthe same thermally mixed and oxidized at 1290° C. to a final Ge contentof about 19% Ge (the temperature of heating is at or near the meltingpoint of the SiGe alloy layer, See FIG. 5). No defects are evident inthe latter image, in fact, extended TEM analysis showed no defects whichsuggests a defect density at or below the 10⁶ cm⁻² range.

FIG. 8 shows the measured SF defect density versus final thickness inthe SGOI fabricated by oxidation at 1200, 1250 and 1320° C. in a mannerconsistent with the '138 application and the present invention. All dataare for 600 Å-17% SiGe initial layers grown on 550 Å SOI substrates. Thefigure shows nearly a two order of magnitude reduction in SF defectdensity using the present invention. Also suggested by the figure is theability to control the SF defect density by controlling the final SGOIthickness.

The SGOI substrate produced using the embodiment of the presentinvention in which oxidation has been maintained within a temperaturefrom about 1230° to about 1320° C. for a time period of less than about2 hours has minimized crosshatching as compared with prior art SGOIsubstrates in which the above protocol is not followed. Moreover, theSGOI substrate material produced in this embodiment has a substantiallyrelaxed SiGe layer that has a stacking fault and/or microtwin density ofless than about 1×10⁵. FIGS. 9 and 10 are 10×10 μm Atomic ForceMicroscope images of an SGOI substrate formed using a prior art thermalmixing process at an oxidation temperature of about 1200° C., and anSGOI substrate formed using the inventive process wherein the oxidationtemperature was performed at a temperature of about 1250° C. for 30minutes, respectively. Note that crosshatching has been minimized inFIG. 10 as compared with FIG. 9. FIG. 11 shows how the pit depthincreases with increasing oxidation time at 1250° C. during theformation of a 400 Å 25% SGOI layer. It should be noted that below about1.5 hours oxidation time, the pits are indistinguishable from theoriginal (before thermal mixing) surface roughness and the data point at30 minutes represents an upper limit of the pit depth.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the scope and spirit ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A substrate material comprising: a Si-containing substrate; aninsulating region that is resistant to Ge diffusion present atop saidSi-containing substrate; and a substantially relaxed SiGe layer presentatop said insulating region, wherein said substantially relaxed SiGelayer has a thickness of about 2000 nm or less, a surface roughness ofless than 15 Å RMS and a defect density of about 10⁷ defects/cm² orless.
 2. The substrate material of claim 1 wherein said insulatingregion is patterned.
 3. The substrate material of claim 1 wherein saidinsulating region is unpatterned.
 4. The substrate material of claim 1wherein said insulating region comprises crystalline or non-crystallineoxides, or crystalline or non-crystalline nitrides.
 5. The substratematerial of claim 1 wherein said insulating region is a buried oxideregion.
 6. The substrate material of claim 1 wherein said substantiallyrelaxed SiGe layer has a measured lattice relaxation of from about 1 toabout 99%.
 7. The substrate material of claim 1 wherein saidsubstantially relaxed SiGe layer has a stacking fault and/or microtwindefect density of less than about 1×10⁵ defects/cm².
 8. The substratematerial of claim 1 wherein said relaxed SiGe layer has surface pitsthat have a depth of less than 30 Å and a width of less than 300 nm. 9.A heterostructure comprising: a Si-containing substrate; an insulatingregion that is resistant to Ge diffusion present atop the Si-containingsubstrate; a substantially relaxed SiGe layer present atop theinsulating region, wherein the substantially relaxed SiGe layer has athickness of about 2000 nm or less, a surface roughness of less than 15Å RMS and a defect density of about 10⁷ defects/cm² or less; and astrained Si layer formed atop the substantially relaxed SiGe layer. 10.The heterostructure of claim 9 wherein said insulating region ispatterned.
 11. The heterostructure of claim 9 wherein said insulatingregion is unpatterned.
 12. The heterostructure of claim 9 wherein saidinsulating region comprises crystalline or non-crystalline oxides, orcrystalline or non-crystalline nitrides.
 13. The heterostructure ofclaim 9 wherein said insulating region barrier layer is a buried oxideregion.
 14. The heterostructure of claim 9 wherein said substantiallyrelaxed SiGe layer has a measured lattice relaxation of from about 1 toabout 99%.
 15. The heterostructure of claim 9 wherein said strained Silayer comprises an epi-Si layer
 16. The heterostructure of Clam 9wherein alternating layers of relaxed SiGe and strained Si are locatedatop said strained Si layer.
 17. The heterostructure of claim 9 whereinsaid strained Si layer is replaced with a lattice mismatched compoundselected from the group consisting of GaAs and GaP.
 18. Theheterostructure of claim 9 wherein said relaxed SiGe layer has surfacepits that have a depth of less than 30 Å and a width of less than 300nm.